The present invention relates to an improved method of preparing catalysts for use in the oxidation of hydrocarbon to prepare dicarboxylic acids and anhydrides. More particularly, this is an improved method of preparing phosphorus - vanadium catalyst.
The present catalyst preparative method provides a simple, easily performed process, which avoids concentrated acid solutions, and corrosive reflux situations. Basically, all of the methods disclosed in the prior art seek to obtain the vanadium in a valence state of less than 5.
A typical catalysts preparation may involve dissolving the vanadium, phosphorus, and other components in a common solvent, such as hot hydrochloric acid and thereafter depositing the solution onto a carrier. The reduced vanadium with a valence of less than 5 is obtained by initially using a vanadium compound with a valence of plus 5 such as V.sub.2 O.sub.5 and thereafter reducing to the lower valence with, for example, hydrochloric acid during the catalyst preparation to form the vanadium oxysalt, vanadyl chloride, in situ. The vanadium compound is dissolved in a reducing solvent, such as hydrochloric acid, which solvent functions not only to form a solvent for the reaction, but also to reduce the valence of the vanadium compound to a valence of less than 5. For example, a vanadium compound, a copper compound, a tellurium compound, phosphorus compound and alk metal compound may be dissolved in any order in a suitable reducing solvent and the formation of the complex allowed to take place. Preferably, the vanadium compound is first dissolved in the solvent and thereafter the phosphorus, copper, tellurium and other metal compounds, if any, are added. The reaction to form the complex may be accelerated by the application of heat. The deep blue color of the solution shows the vanadium has an average valence of less than 5. The complex formed is then, without a precipitation step, deposited as a solution onto a carrier and dried. In this procedure, the vanadium has an average valence of less than plus 5, such as about plus 4, at the time it is deposited onto the carrier. Generally, the average valence of the vanadium wil be between about plus 2.5 and 4.6 at the time of deposition onto the carrier.
In another method the catalyst is prepared by precipitating the metal compounds, either with or without a carrier, from a colloidal dispersion of the ingredients in an inert liquid. In some instances the catalyst may be deposited as molten metal compounds onto a carrier; however, care must be taken not to vaporize off any of the ingredients such as phosphorus. The catalysts have also been prepared by heating and mixing anhydrous forms of phosphorus acids with vanadium compounds, copper compounds, Me compounds, and the alk - metal compound. The catalysts may be used as either fluid bed or fixed bed catalysts. In any of the methods of preparation, heat may be applied to accelerate the formation of the complex.
Another example of the catalyst preparation is to mix with heating at a temperature of about 100.degree. to 600.degree. C. an anhydrous phosphoric acid such as ortho-phosphoric acid, pyrophosphoric acid, triphosphoric acid or metaphosphoric acid with a vanadium compound such as vanadium pentoxide or ammonium metavanadate, a copper compound such as copper (II) chloride, a Me compound such as tellurium tetrachloride and an alkali such as potassium chloride. After the exothermic reaction between the ingredients the catalyst may be used. The reaction mixture may be formed onto carriers or shaped into forms such as pellets prior to the reaction to form the catalyst.
Another example of the preparation of the catalyst complex is to dissolve the copper, Me and alk metal compounds and a vanadium compound such as ammonium metavanadate or vanadium pentoxide in an aqueous solution of phosphoric acid. After the components have been dissolved the solution is heated until precipitation occurs. The precipitant can then be dried and used as a catalyst, or a carrier may be combined with the liquid phase either before or after the precipitation.
It is an advantage of the present invention that concentrated solutions of strong acids are not employed. It is a further advantage of the present process that rigorous refluxing of the components to reduce the vanadium portion thereof is not required. A feature of the present invention is its simplicity of operation. These and other advantages and features of the present invention will be clearly apparent from the following discussion.